1. Field of the Invention
The present invention relates to a medical device according to the preamble of claim 1.
2. Description of the Prior Art
A substance known as surfactant is found in healthy lungs. An essential function performed by surfactant is the reduction of surface tension so that all of the alveoli can be kept open. Surfactant contains a number of proteins, the individual functions of which are not entirely understood. The main constituents, however, are known and include four different proteins. These proteins are usually named SP-A, SP-B, SP-C, and SP-D.
Different types of lung trauma influence the occurrence of surfactant, such as by a reduction in the total amount of surfactant (the creation of surfactant in the lungs is influenced) and in part by a change in the occurrence of one or more of the main proteins SP-A, SP B, SP-C, and SP-D. The consequence of the change in the occurrence of surfactant is in most cases a stiffer (less pliant) lung, often with an unknown number of alveoli that have collapsed. Gas exchange is quickly worsened as a result and the patient risks becoming dependent on mechanical ventilation in order to survive.
A more complete background description of the role played by surfactant and the physiological interplay is provided in U.S. Pat. No. 6,020,307.
An obvious treatment of surfactant deficiency is to supply exogenous surfactant, however this is not entirely without consequence. A completely synthetic surfactant is presently unavailable. Natural surfactant is manufactured from animal lungs but is expensive. The price of natural surfactant is in the region of £200 per milliliter (ml). The recommended dosage is 1.25 ml per kilogram bodyweight. For a child weighing 2 kg the cost of one dose is circa £500 but for an adult of 60 kg the cost of a dose is closer to £15,000. Dosing normally needs repeating several times during a treatment. Natural surfactant therefore cannot be used as a general treatment method, at least not for adult patients. At the same time it is true that a portion of the exogenous surfactant is forced from the lungs during expiration. This is at least in part due to the change in alveolar volume during expiration. It can also be assumed that a part of the added surfactant never reaches the alveoli and do not provide any therapeutic effect.
Although analysis methods are known to distinguish between the different proteins it is not possible to undertake continual or frequent analysis of the condition for every single patient. This is primarily because samples of surfactant are extracted from the lungs using bronchial washes or mucous suction. Both of these methods normally involve the discontinuation of the mechanical ventilation of the patient and in the worst case the patient must be disconnected from the ventilator.
There therefore exists a desire to improve the management of surfactant deficiency. A first goal is to provide more effective procedures that make possible less expensive and more effective treatment. A second goal is better and more effective sample taking that can be carried out relatively continuously. A third goal is a better and more effective means for the dosing of surfactant.
Additionally, sampling of substances related to the function and/or condition of the lungs may relate to substances other than the surfactant components mentioned above.